This invention relates to a twisting ball display sheet containing bichromal balls, and more particularly, to a mechanism utilized in a twisting bichromal ball display sheet to rotate the twisting balls without using Zeta potential.
A twisting ball display sheet comprises a thin transparent sheet which has many attributes of a paper document. It looks like paper, has ambient light valve behavior like paper (for example, the brighter the ambient light, the more easily it may be seen), is flexible like paper, can be carried around like paper, can be copied like paper, and has nearly the archival memory of paper.
Referring to FIG. 1, there is shown a cross sectional view of a portion of a prior art twisting ball display sheet 10 which comprises a plurality of bichromal balls B which have a black hemisphere b on one side and a white hemisphere w on the other side. Such a display is disclosed in the U.S. Pat. No. 4,126,854 titled "Twisting Ball Panel Display".
Typically, the bichromal balls B consist of pigmented particles suspended in a substantially transparent sheet 12 made from a material such as elastomer. Each ball B is located in a cavity 14 within the transparent sheet 12. The cavities are slightly larger than the size of the balls B such that each ball B has freedom to rotate or otherwise move slightly within its cavity. The volume 16 of each cavity 14 not occupied by a ball B is filled with a dielectric liquid.
In FIG. 1, looking at the display sheet 10 from the top in the direction shown as d, since only the white hemispheres w of all the balls B are visible, the display sheet is seen as a blank display sheet (assuming that the background of the display sheet is white). Once a ball B is rotated to have its black hemisphere visible, a black dot on the display sheet will be generated. The balls B can be selectively rotated to display a desired image or text.
Currently, several mechanisms are used to create a dipole moment to rotate the balls in a twisting ball display sheet. Typically, they rely on electrical anisotropy due to hemispherical surface coatings of different Zeta potential and their distribution in a volume of a dielectric liquid.
It is an object of this invention to use a different mechanism than Zeta potential to provide a greater dipole moment.